Certain prior art welding systems use bridge topologies in a welding power source to provide AC welding capability. A half-bridge topology may be used in a welding power source having dual output current paths configured to share a common path, such that each output can induce a flow of opposite polarity in the shared path. In practice, many welding power sources are configured as such and may require only the addition of a second set of rectifier devices to complete the second path. A switch may be placed in the non-shared path of each power source leg and the direction of current flow through a connected welding output circuit path is determined by the active leg. A full bridge topology may be used with just about any power source topology, providing flexibility and the potential to be added to existing designed power sources. The full bridge topology allows easy implementation of zero cross assisting circuits. A blocking diode may be used to protect the devices in the power source from high voltage transients that occur during the zero cross. For many welding processes such as, for example, an AC gas tungsten arc welding (GTAW or TIG) process or a gas metal arc welding (GMAW or MIG) process, it is desirable for the arc between the electrode and the workpiece to quickly re-ignite in the opposite polarity direction when the welding current crosses zero.
A welding power source may have a maximum voltage level (e.g., 100 VDC) that it is designed to output. When an AC welding current crosses zero (i.e., changes polarity), a higher voltage (e.g., 300 VDC) may be demanded from the power source than the power source can provide, to keep the arc lit and make the arc more stable when the arc current is low, and to re-ignite the arc between the electrode and the workpiece. As a result, the arc may extinguish and not re-establish. In TIG welding (where there is no wire electrode), if the arc extinguishes, the welding power source may have to repeat the entire arc-establishment process before welding can continue, resulting in an inefficient welding process. In general, the plasma column associated with low current arc welding tends to be unstable and can result in undesired arc outages.
Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such systems and methods with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings.